The present invention relates generally to vehicles with hybrid propulsion systems, and more particularly to a combination of a gas turbine-based propulsion system and a stored electric-based power system that cooperates with rotational lift or thrust-producing devices to permit a vehicle to operate in numerous modes of movement.
Aircraft are broadly categorized as either fixed-wing vehicles (such as an airplane) or rotary-wing vehicles (such as helicopters and autogyros, the latter also referred to as autogyros or gyrocopters). Gas turbine engines (which are one form of internal combustion engine) are widely used to power both the fixed-wing and rotary wing forms of aircraft, where fixed-wing vehicles often employ turbofan, turbojet and turboprop variants, and rotary-wing vehicles often employ turboshaft variants. In all circumstances, the basic gas generator hardware is common, including a compressor, a combustor and turbine, where the compressor and turbine rotate on a generally common shaft (or set of concentric shafts) such that energy extracted from the turbine is used to power the compressor. Turbofans are very similar to turbojets, with the exception that they typically include an additional fan located upstream of the compressor. A turboprop engine, in addition to including the respective turbofan or turbojet componentry, also includes a fore-mounted drive shaft that spins in common with the shaft of the compressor and turbine. To match the high rotational speed of the compressor and turbine to that of a propeller, a gearbox is inserted between the front end of the drive shaft and a propeller shaft. Turboshafts also include similar components to the turbofans and turbojets, and additionally include a shaft rotatably responsive to another turbine stage. Both fixed-wing and rotary-wing vehicles contain advantages and disadvantages. The present invention seeks to combine these types of aircraft into one which can selectively take advantage of fixed or rotary-winged aircraft.
In turboshaft engines, power generated by the gas generator (which is spinning about a generally horizontal axis) is transferred to the shaft (which is spinning about a generally vertical axis such that it can turn a rotor made up of a series of blades that radially extend from a central hub) through a gearing mechanism, such as a beveled or worm gear. Shaft horsepower needs to produce a particular rotor rotational speed that varies depending on the aircraft type, size and intended mission. For example, the CH-47 Chinook is a popular twin-rotor helicopter designed for commercial and military heavy lifting. Rotor blade power requirements for helicopters such as this may be in the range of five thousand horsepower, while speed requirements of around two hundred and twenty five revolutions per minute (RPM) are typical.
Despite their widespread use, conventional gas turbine-based propulsion systems have significant drawbacks for certain types of aircraft. For example, in the event a turboshaft engine fails, a helicopter, gyrocopter or other inherently unstable aircraft has no way of returning to earth under its own power, and at best can expect to have to endure a controlled crash landing. Likewise, if a helicopter employing a turboshaft engine as propulsive power is flying or hovering over an area where terrorists, armed conflict or related hostilities exist, the extreme heat put out by the engine or engines may make the helicopter exceedingly vulnerable to attack from infrared (IR) seeking weaponry. Furthermore, to the extent that there are existing rotary-winged aircraft (such as the Bell Boeing V-22 Osprey) that are configured to operate in both a helicopter mode of operation and in a fixed-wing aircraft mode of operation, significant mechanical complications abound, including the necessity of tilting the entire wing in order to shift between modes. Moreover, such a configuration does not provide the ability to operate as a gyrocopter, where additional fuel economy and related range may be possible. In addition, in situations where power may be lost, there is no ability with a design where the propeller is directly coupled to the engine to shift the rotors into a freewheeling position; this in turn imperils slow, controlled aircraft descents for emergency landings. Accordingly, there exists a need for an aircraft and a propulsion system that overcomes these and other shortcomings.